Engine

ABSTRACT

An engine operable in a premixed combustion system and a diffusion combustion system. The engine includes a main fuel injection valve, a pilot fuel injection valve, a liquid fuel tank, a main fuel supply path, a pilot fuel supply path, a pilot fuel filter, a pilot fuel high-pressure pump, a pilot fuel tank, and a pilot fuel supply pump. The pilot fuel tank stores pilot fuel sent from the pilot fuel high-pressure pump and not injected by the pilot fuel injection valve. This pilot fuel is sent to an automatic backwash filter and a pilot fuel filter while not passing through the liquid fuel tank.

CROSS-REFERENCE

This is a continuation of US patent application, application Ser. No.17/347,464, filed Jun. 14, 2021, which is a continuation of applicationSer. No. 16/892,224, filed Jun. 3, 2020, which is a continuation ofapplication Ser. No. 16/316,791, with the § 371 (1), (2) date of Jan.10, 2019, which is a national phase entry of PCT/JP2017/022728 filed onJun. 20, 2017, which claims priority to Japanese Patent Application,JP2016-139446, fled on Jul. 14, 2016. The documents cited herein are allincorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an engine employing multiple types offuel.

BACKGROUND ART

A known so-called dual fuel engine is capable of being driven whileselecting one of a premixed combustion system in which fuel gas such asnatural gas is mixed with air for combustion and a diffusion combustionsystem in which liquid fuel (fuel oil) such as heavy oil is diffused forcombustion. Patent Literature 1 (PTL 1) discloses a dual fuel engine.

The dual fuel engine of PTL 1 includes a fuel injection valve thatsupplies fuel to combustion chambers during combustion in the diffusioncombustion system and supplies fuel to the combustion chambers in orderto ignite gaseous fuel during combustion in the premixed combustionsystem.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent Application Laid-Open No. 2002-4899

SUMMARY OF INVENTION Technical Problem

In PTL 1, fuel is injected from the same fuel injection valve in boththe diffusion combustion system and the premixed combustion system.However, the diffusion combustion system and the premixed combustionsystem have different purposes of fuel injection, and thus, cannotachieve optimum fuel injection in some cases when employing the samefuel injection valve.

In view of this, a configuration using different fuel injection valvesbetween the diffusion combustion system and the premixed combustionsystem has been proposed. An engine of this type uses two types of fuelinjection valves, and thus, needs two types of fuel supply paths. Forthe engine of this type, however, no specific fuel paths designed inconsideration of fuel purification have been disclosed to date.

Some aspects of the present invention have been made in view of theforegoing circumstances, and have an object of providing a fuel pathdesigned in consideration of fuel purification in an engine usingdifferent fuel injection devices between a diffusion combustion systemand a premixed combustion system.

Solution to Problem and Advantages

Problems to be solved by the invention are as described above, and next,means for solving the problems and advantages thereof will be described.

In an aspect of the invention, an engine having the followingconfiguration is provided.

That is, the engine is operable in a premixed combustion system in whichgaseous fuel mixed with air is caused to flow into a combustion chamberand a diffusion combustion system that injects liquid fuel into thecombustion chamber for combustion. The engine includes a main fuelinjection valve, a pilot fuel injection valve, a liquid fuel tank, amain fuel supply path, a pilot fuel supply path, a pilot fuel filter, apilot fuel high-pressure pump, a pilot fuel tank, and a pilot fuelsupply pump. The main fuel injection valve supplies liquid fuel to thecombustion chamber during combustion in the diffusion combustion system.The pilot fuel injection valve supplies liquid fuel as pilot fuel to thecombustion chamber in order to ignite gaseous fuel during combustion inthe premixed combustion system. The liquid fuel tank stores liquid fuel.The main fuel supply path supplies liquid fuel stored in the liquid fueltank to the main fuel injection valve. The pilot fuel supply pathsupplies liquid fuel stored in the liquid fuel tank as pilot fuel to thepilot fuel injection valve. The pilot fuel filter is disposed in anintermediate portion of the pilot fuel supply path. The pilot fuelhigh-pressure pump is disposed in an intermediate portion of the pilotfuel supply path and sends, to the pilot fuel injection valve, pilotfuel that has passed through the pilot fuel filter. The pilot fuel tankis disposed in an intermediate portion of the pilot fuel supply path andstores pilot fuel sent from the pilot fuel high-pressure pump and notinjected by the pilot fuel injection valve. The pilot fuel supply pumpis disposed in an intermediate portion of the pilot fuel supply path andsends, to the pilot fuel filter, pilot fuel stored in the pilot fueltank.

Accordingly, uninjected pilot fuel does not return to the liquid fueltank and is supplied to the pilot fuel injection valve again. Thus,pilot fuel purified by the pilot fuel filter is not easily mixed withliquid fuel in the liquid fuel tank. Consequently, even with a lowcleanliness of liquid fuel stored in the liquid fuel tank, themaintenance frequency of the pilot fuel filter can be reduced.

The engine preferably has the configuration as follows. Specifically,the engine includes a fuel purification path. The fuel purification pathis a path for circulation through a purification filter for purifyingpilot fuel and the pilot fuel tank.

Accordingly, pilot fuel is also purified by the purification filter, andthus, the maintenance frequency of the pilot fuel filter can be furtherreduced.

In the engine, the pilot fuel supply path and the fuel purification pathpreferably partially overlap each other.

Accordingly, since the two paths overlap, the length of fuel pipes canbe reduced. In addition, a pressure loss occurring when fuel flowsthrough the fuel pipes can be reduced.

In the engine, the purification filter is preferably an automaticbackwash filter having a filtration efficiency lower than that of thepilot fuel filter.

Accordingly, the pilot fuel filter only needs to remove foreignsubstances not removed by the purification filter, and thus, themaintenance frequency of the pilot fuel filter can be further reduced.

The engine preferably has the configuration as follows. Specifically,the engine further includes a pilot fuel supply common rail pipe and amain fuel filter. The pilot fuel supply common rail pipe is disposed inan intermediate portion of the pilot fuel supply path, and suppliespilot fuel to the pilot fuel injection valve at a pressure higher thanthat a pressure at which liquid fuel is supplied to the main fuelinjection valve. The main fuel filter is disposed in an intermediateportion of the main fuel supply path. The pilot fuel filter has afiltration efficiency higher than that of the main fuel filter.

Accordingly, clogging with pilot fuel injected at high pressure can bemore efficiently prevented or reduced, and gaseous fuel can be ignitedwith reliability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A view schematically illustrating an engine according to oneembodiment of the present invention.

FIG. 2 A rear view of an engine body

FIG. 3 A partial rear cross-sectional view illustrating a configurationaround a combustion chamber in detail.

FIG. 4 A front view of the engine body.

FIG. 5 A plan view of the engine body.

FIG. 6 A right side view of the engine body.

FIG. 7 A schematic front perspective view illustrating a liquid fuelsupply path.

FIG. 8 A left side surface of the engine body.

FIG. 9 A perspective view of the engine body illustrating a state wherea part of a side cover and a heat shielding cover are detached.

FIG. 10 A schematic view for describing a fuel supply path that suppliesfuel oil to the engine body

FIG. 11 A schematic view for describing a fuel supply path that suppliesfuel oil to an engine body according to a variation.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described with referenceto the drawings. FIG. 1 is a view schematically illustrating an engine100 according to one embodiment of the present invention. FIG. 2 is arear view of an engine body 21. FIG. 3 is a partial rear cross-sectionalview illustrating a configuration around a combustion chamber 110 indetail. FIG. 4 is a front view of the engine body 21. FIG. 5 is a planview of the engine body 21. FIG. 6 is a right side view of the enginebody 21 FIG. 7 is a schematic front perspective view illustrating aliquid fuel supply path. FIG. 8 is a left side view of the engine body21. FIG. 9 is a perspective view of the engine body 21 illustrating astate where a part of a side cover 43 and a heat shielding cover 45 aredetached.

The engine 100 (engine with a fuel supply system) according to thisembodiment illustrated in FIG. 1 is a so-called dual fuel engineoperable in both a premixed combustion system in which gaseous fuelmixed with air is caused to flow into combustion chambers and adiffusion combustion system that injects liquid fuel into combustionchambers for combustion. The engine 100 according to this embodimentincludes an engine body 21 that generates a driving force using suppliedfuel. The engine body 21 serves as a driving source of a propulsive andpower generating mechanism of an unillustrated ship and is mounted to aninner bottom plate of an engine room of the ship with a base interposedtherebetween.

A crank shaft 24 serving as an engine output shaft projects rearwardfrom a rear end of the engine body 21. An unillustrated speed-reducer iscoupled to one end of the crank shaft 24 to enable power transfer. Thespeed reducer is sandwiched between the crank shaft 24 and anunillustrated propeller shaft of the ship, and the propeller shaft isdisposed coaxially with the crank shaft 24. A propeller for generatingpropulsive power of the ship is attached to an end of the propellershaft. The speed-reducer includes a PTO shaft, and an unillustratedshaft-driving power generator is coupled to the PTO shaft to enablepower transfer.

This configuration enables a driving force of the engine body 21 to bebranched into the propeller shaft and the shaft-driving power generatorand transferred through the speed-reducer. Accordingly, propulsive powerof the ship is generated, and electric power generated by driving theshaft-driving power generator is supplied to electric circuits in theship.

Next, the engine 100 will be described in detail with reference to thedrawings. The engine 100 is a dual fuel engine as described above, andcan be driven while selecting one of a premixed combustion system inwhich fuel gas such as natural gas is mixed with the air for combustionand a diffusion combustion system in which liquid fuel (fuel oil) suchas heavy oil is diffused for combustion.

Positional relationship will be described below with a side connected tothe speed-reducer (a side where a flywheel is disposed) being defined asrear, the opposite side being defined as front of the engine body 21. Inthis positional relationship, left and right toward the front surface(front) of the engine body 21 are respectively defined as left and rightof the engine body 21. Accordingly, the front-rear direction(longitudinal direction) can be a direction parallel to the axis of thecrank shaft 24, and the left-right direction (lateral direction) can bea direction perpendicular to the axis of the crank shaft 24. It shouldbe noted that this description is not intended to limit the orientationof the engine body 21, and the engine body 21 can be placed in variousorientations in accordance with application and others.

As illustrated in FIG. 1 , a gaseous fuel supply path 30 and a liquidfuel supply path 31 are connected to the engine body 21. A gaseous fueltank 32 for storing liquefied natural gas (LNG) is connected to thegaseous fuel supply path 30, whereas a liquid fuel tank 33 for storingmarine diesel oil (MDO) is connected to the liquid fuel supply path 31.In this configuration, the gaseous fuel supply path 30 supplies fuel gasto the engine body 21, and the liquid fuel supply path 31 supplies fueloil to the engine body 21.

In the gaseous fuel supply path 30, a gaseous fuel tank 32 that storesgaseous fuel in a liquefied state, a vaporizing device 34 that vaporizesthe liquefied fuel in the gaseous fuel tank 32, and a gas valve unit 35that adjusts the supply rate of fuel gas from the vaporizing device 34to the engine body 21, are arranged in this order from the upstreamside.

As illustrated in FIGS. 2 through 4 , the engine body 21 is an in-linemulti-cylinder engine configured by mounting cylinder heads 26 onto acylinder block 25. The crank shaft 24 is rotatably supported on a lowerportion of the cylinder block 25 with an axis 24 c oriented in thefront-rear direction as illustrated in FIGS. 2 and 4 .

In the cylinder block 25, a plurality of (six in this embodiment)cylinders are arranged in a line (in series) along the axis of the crankshaft 24. As illustrated in FIG. 3 , each cylinder houses a piston 78such that the pistons 78 are slidable in the top-bottom direction. Thispiston 78 is coupled to the crank shaft 24 through an unillustrated rod.

As illustrated in FIGS. 5 and 6 , the plurality of (six in thisembodiment) cylinder heads 26 are attached to the cylinder block 25 tocover the cylinders individually from above. The cylinder heads 26 areprovided to the individual cylinders, and are fixed to the cylinderblock 25 using head bolts 99. As illustrated in FIG. 3 , in eachcylinder, the combustion chamber 110 is defined in space surrounded bythe upper surface of the piston 78 and the cylinder head 26.

As illustrated in FIG. 5 , a plurality of head covers 40 correspond tothe individual cylinders and are arranged on the cylinder heads 26 in aline along the direction of the axis 24 c of the crank shaft 24(front-rear direction). As illustrated in FIG. 3 , each of the headcovers 40 houses a valve mechanism constituted by a push rod, a rockerarm, and so forth in order to operate an intake valve and an exhaustvalve. In a state where the intake valves are open, intake air from anintake manifold 67 can be taken in the combustion chambers 110. In astate where the exhaust valves are open, exhaust air from the combustionchambers 110 can be emitted to an exhaust manifold 44.

As illustrated in FIG. 3 , the upper end of a pilot fuel injection valve82 described later is disposed near the left of each head cover 40. Withrespect to an imaginary vertical plane P1 (see FIG. 7 ) including theaxis 24 c of the crank shaft 24, the pilot fuel injection valves 82 areinserted in the cylinder heads 26 from one side (from the left in thisembodiment) of the imaginary vertical plane P1 and extend obliquelydownward toward the combustion chambers 110.

In the following description, a location at one side/the other side ofthe imaginary vertical plane P1 including the axis 24 c of the crankshaft 24 will be sometimes referred to as a location at one side/theother side of the crank shaft 24. The imaginary vertical plane P1 can bean infinite plane in both the direction of the axis 24 c of the crankshaft 24 and the top-bottom direction, but FIG. 7 shows only a part ofthe imaginary vertical plane P1 near the engine body 21 for convenienceof expression in the perspective view.

As illustrated in FIGS. 2, 3, 8 , a gas manifold 41 for distributing andsupplying gaseous fuel to the combustion chambers 110 of the cylindersduring combustion in the premixed combustion system is provided at theleft of the cylinder heads 26. The gas manifold 41 extends in thefront-rear direction along the left side surfaces of the cylinder heads26. The plurality of (six in this embodiment) gas branch pipes 41 acorresponding to the combustion chambers 110 of the cylinders areconnected to the gas manifold 41, and as illustrated in FIG. 3 , gasinjectors 98 for injecting gaseous fuel are provided at the front endsof the gas branch pipes 41 a. The front ends of the gas injectors 98face intake branch pipes 67 a corresponding to the cylinders and formedinside the cylinder heads 26. By injecting gaseous fuel from the gasinjectors 98, the gaseous fuel can be supplied to the intake branchpipes 67 a of the intake manifold 67.

As illustrated in FIGS. 3, 7, and 9 , a liquid fuel supply rail pipe 42for distributing and supplying liquid fuel to the combustion chambers110 of the cylinders during combustion in the diffusion combustionsystem is disposed at the right of the cylinder block 25. The liquidfuel supply rail pipe 42 extends in the front-rear direction along theright side surface of the cylinder block 25. Liquid fuel supplied to theliquid fuel supply rail pipe 42 is distributed and supplied to main fuelinjection pumps 89 corresponding to the cylinders. As illustrated inFIG. 3 , each cylinder is provided with a main fuel injection valve 79that injects liquid fuel supplied from the main fuel injection pump 89.The main fuel injection valves 79 are inserted in the cylinder heads 26vertically from above the cylinder heads 26, the upper ends of the mainfuel injection valves 79 are disposed inside the head covers 40, and thelower ends of the main fuel injection valves 79 face the combustionchambers 110 of the cylinders. The main fuel injection pumps 89 and themain fuel injection valves 79 are connected to each other through liquidfuel supply paths 106 formed in the cylinder heads 26.

A liquid fuel return aggregate pipe 48 for collecting redundant fuelreturned from the main fuel injection pumps 89 is disposed near thebottom of the liquid fuel supply rail pipe 42. The liquid fuel returnaggregate pipe 48 is disposed in parallel with the liquid fuel supplyrail pipe 42, and connected to the main fuel injection pumps 89. A fuelreturn pipe 115 for returning liquid fuel to the liquid fuel tank 33 isconnected to an end of the liquid fuel return aggregate pipe 48.

As illustrated in FIGS. 3, 7 and 9 , a pilot fuel supply rail pipe(pilot fuel supply common rail pipe) 47 for distributing and supplyingpilot fuel to the combustion chambers 110 of the cylinders in order toignite gaseous fuel during combustion in the premixed combustion systemis disposed at the right of the cylinder block 25 and above the liquidfuel supply rail pipe 42. The pilot fuel supply rail pipe 47 extends inthe front-rear direction along the right side surface of the cylinderblock 25. As illustrated in FIGS. 3 and 7 , the cylinders are providedwith the pilot fuel injection valves 82 for injecting liquid fuel (pilotfuel) supplied from the pilot fuel supply rail pipe 47. The pilot fuelinjection valves 82 are inserted in the cylinder heads 26 verticallyfrom above the cylinder heads 26, the upper ends of the pilot fuelinjection valves 82 are disposed immediately at the left side of thehead covers 40, and the lower ends of the pilot fuel injection valves 82face the combustion chambers 110 of the cylinders. As illustrated inFIG. 7 , pilot fuel branch pipes 109 corresponding to the cylindersbranch off from the pilot fuel supply rail pipe 47. The pilot fuelbranch pipes 109 pass between the head covers 40 arranged side by side,and are connected to the upper ends of the pilot fuel injection valves82. The pilot fuel branch pipes 109 are covered with a branch pipe cover105 for preventing leaked fuel from scattering.

As illustrated in FIGS. 3, 7, and 9 , a step is formed on an upperportion of the right side surface of the engine body 21 constituted bythe cylinder block 25 and the cylinder heads 26. The pilot fuel supplyrail pipe 47, the liquid fuel supply rail pipe 42, and the main fuelinjection pumps 89 are disposed on this step. A side cover 43 isattached to the cylinder block 25 and the cylinder heads 26 to cover thestep. The pilot fuel supply rail pipe 47, the liquid fuel supply railpipe 42, and the main fuel injection pumps 89 are covered with the sidecover 43 FIG. 9 illustrates a state where a part of the side cover 43 isdetached.

As illustrated in FIGS. 2, 3, and 9 , the exhaust manifold 44 forcollecting exhaust air generated by combustion in the combustionchambers 110 of the cylinders and emitting the exhaust air to theoutside is disposed in parallel with the gas manifold 41 above the leftof cylinder heads 26 and above the gas manifold 41. The outer peripheryof the exhaust manifold 44 is covered with a heat shielding cover 45(where the heat shielding cover 45 is detached in FIG. 9 ). Asillustrated in FIG. 3 , exhaust branch pipes 44 a corresponding to thecylinders are connected to the exhaust manifold 44. The exhaust branchpipes 44 a communicate with the combustion chambers 110 of thecylinders.

The intake manifold 67 for distributing and supplying outside air(intake air) to the combustion chambers 110 of the cylinders is disposedin parallel with the gas manifold 41 inside the cylinder block 25 andnear the left of the cylinder block 25. As illustrated in FIG. 3 , thesix intake branch pipes 67 a branching off from the intake manifold 67are formed inside the cylinder heads 26 and communicate with theindividual combustion chambers 110.

With this configuration, in combustion in the diffusion combustionsystem, an appropriate amount of liquid fuel is injected from the mainfuel injection valves 79 into the combustion chambers 110 at anappropriate timing when air supplied to the cylinders from the intakemanifold 67 is compressed by sliding of the pistons 78. Injection ofliquid fuel into the combustion chambers 110 causes the pistons 78 toreciprocate in the cylinders with propulsive power obtained bycombustion in the combustion chambers 110, and the reciprocatingmovement of the pistons 78 is converted to rotation movement of thecrank shaft 24 through a rod, thereby obtaining a driving force.

On the other hand, in combustion in the premixed combustion system,gaseous fuel from the gas manifold 41 is injected from the gas injectors98 into the intake branch pipes 67 a so that air supplied from theintake manifold 67 and the gaseous fuel are mixed. At an appropriatetiming when the air mixture of the air introduced into the cylinders andthe gaseous fuel is compressed by sliding of the pistons 78, a smallamount of pilot fuel is injected from the pilot fuel injection valves 82into the combustion chambers 110 so that the gaseous fuel is ignited.The pistons 78 reciprocates in the cylinders with propulsive powerobtained by combustion in the combustion chambers 110, and thereciprocating movement of the pistons 78 is converted to rotationmovement of the crank shaft 24 through the rod, thereby obtaining adriving force.

In either case of combustion in the diffusion combustion system andcombustion in the premixed combustion system, exhaust air generated bycombustion is pushed out from the cylinders by movement of the pistons78, and collected in the exhaust manifold 44, and then emitted to theoutside.

As illustrated in FIG. 4 , a cooling water pump 53, a lubricating oilpump 55, and a pilot fuel high-pressure pump 56 are disposed at thefront end surface (front surface) of the engine body 21 and surround afront end portion of the crank shaft 24. The pilot fuel high-pressurepump 56 is disposed near the right of the crank shaft 24. A front endportion of the engine body 21 is provided with an unillustrated rotationtransfer mechanism that transfers a rotative force of the crank shaft24. Accordingly, a rotative force of the crank shaft 24 is transferredthrough the rotation transfer mechanism so that the cooling water pump53, the lubricating oil pump 55, and the pilot fuel high-pressure pump56 provided at the outer periphery of the crank shaft 24 are therebydriven.

As illustrated in FIG. 8 , a lubricating oil cooler 58 and a lubricatingoil strainer 59 are attached to the left side surface of the cylinderblock 25. Lubricating oil supplied from the lubricating oil pump 55 iscooled by the lubricating oil cooler 58, then purified by thelubricating oil strainer 59, and supplied to components of the enginebody 21.

Cooling water sent from the cooling water pump 53 illustrated in FIG. 4cools cylinders of the engine body 21, and then is collected to anover-cylinder head cooling water pipe 46 illustrated in, for example,FIG. 5 .

The intercooler 51 is disposed along the front end of the engine body21, and cools air compressed by a compressor of the turbocharger 49. Asillustrated in FIG. 8 , a cylinder block left cooling water pipe 60extends rearward from ahead of the cylinder block 25 along the gasmanifold 41 to a position between the lubricating oil cooler 58 and thelubricating oil strainer 59, and supplies cooling water to thelubricating oil cooler 58.

As illustrated in FIGS. 5 and 9 , the over cylinder head cooling waterpipe 46 is disposed in parallel with the exhaust manifold 44 and locatedbetween a plurality of head covers 40 above the cylinder heads 26 andthe exhaust manifold 44. The over cylinder head cooling water pipe 46 iscoupled to cooling water branch pipes corresponding to the cylinders,and is connected to cooling water channel of the cylinders (coolingwater channels formed in the cylinder heads 26) through the coolingwater branch pipes.

The pilot fuel high-pressure pump 56 illustrated in FIG. 4 is driven torotate to thereby increase the pressure of fuel oil (liquid fuel)supplied from the liquid fuel tank 33 illustrated in FIG. 1 by anunillustrated fuel feed pump, and sends the fuel oil to the pilot fuelsupply rail pipe 47 by way of the pilot fuel supply main pipe 107illustrated in, for example, FIG. 7 . Pilot fuel filters 141 forfiltering fuel oil are provided in an intermediate portion of a fuelpath from the liquid fuel tank 33 to the pilot fuel high-pressure pump56.

The unillustrated fuel feed pump (different from the pilot fuelhigh-pressure pump 56) is driven by a motor so that the fuel feed pumpsucks fuel oil from the liquid fuel tank 33 and sends the oil to theliquid fuel supply rail pipe 42 by way of the liquid fuel supply mainpipe 108 illustrated in, for example, FIG. 7 . Main fuel filters 131 forfiltering fuel oil are disposed in an intermediate portion of a supplypath of fuel oil from the liquid fuel tank 33 to the liquid fuel supplyrail pipe 42.

As illustrated in FIG. 7 , the pilot fuel supply main pipe 107, theliquid fuel supply main pipe 108, and the fuel return pipe 115 aredisposed immediately ahead of the cylinder block 25 and extend along theright side surface of the cylinder block 25. The pilot fuel supply mainpipe 107, the liquid fuel supply main pipe 108, and the fuel return pipe115 extend in the top-bottom direction along the right side surface ofthe cylinder block 25 through a plurality of clamp members 11Iprojecting rightward from the front end surface of the cylinder block25.

An engine-side operation control device 71 for performing control suchas start and stopping of the engine body 21 is disposed toward the rightand ahead of the cylinder heads 26, more specifically, on the right sidesurface of the intercooler 51 with a stay interposed therebetween (seeFIGS. 6 and 9 ). The engine-side operation control device 71 includes anoperation section such as a switch that accepts start and stopping ofthe engine body 21 by an operator, and a display that displays anoperating state of the engine body 21. The operator operates theengine-side operation control device 71 to thereby drive the engine body21 in one of the premixed combustion system and the diffusion combustionsystem.

Next, configurations of the main fuel filters 131 and the pilot fuelfilters 141 and a configuration around these filters will be morespecifically described with reference to FIG. 10 . FIG. 10 is aschematic view for describing the liquid fuel supply path 31 thatsupplies fuel oil to the engine body 21.

As illustrated in FIG. 10 , in this embodiment, the liquid fuel supplypath 31 that supplies fuel oil can be divided into two paths(specifically circulation paths) a main fuel supply path 121 thatsupplies fuel to the main fuel injection valves 79 and a pilot fuelsupply path 122 that supplies fuel to the pilot fuel injection valves82. The engine 100 includes a fuel purification path 123 for purifyingfuel oil to be supplied to the pilot fuel injection valves 82.

In the main fuel supply path 121, a main fuel pump 161, the main fuelfilters 131, main fuel injection pumps 89, main fuel injection valves79, a main pressure retention valve 162, and an air separator 163 arearranged in this order from an upstream side in the flow direction offuel oil.

Fuel oil (liquid fuel) in the liquid fuel tank 33 is sucked by the mainfuel pump 161 disposed in the engine body 21. Fuel oil emitted from themain fuel pump 161 is supplied to the main fuel injection valves 79through the main fuel supply path 121. The main fuel supply path 121includes, for example, the liquid fuel supply main pipe 108, the liquidfuel supply rail pipe 42, the liquid fuel supply paths 106, the liquidfuel return aggregate pipe 48, and the fuel return pipe 115 describedabove. As illustrated in FIG. 10 , redundant fuel oil returned from themain fuel injection pumps 89 is returned to the air separator 163 by wayof the liquid fuel return aggregate pipe 48 and the fuel return pipe115. The air separator 163 removes air included in liquid fuelcirculating in the main fuel supply path 121. The air separator 163 isdisposed on the main fuel supply path 121 and at an intersection of apath toward the main fuel injection pumps 89 and a path from the mainfuel injection pumps 89. Thus, liquid fuel returned from the main fuelinjection pumps 89 and liquid fuel newly supplied from the liquid fueltank 33 are combined together inside the air separator 163. Accordingly,the combined liquid fuel circulates in the main fuel supply path 121.The main pressure retention valve 162 for retaining the pressure of thereturned fuel is disposed between the fuel return pipe 115 and theliquid fuel tank 33.

The main fuel filters 131 are disposed in an intermediate portion of themain fuel supply path 121 in order to remove foreign substancescontained in liquid fuel. Specifically, the main fuel filters 131 filterliquid fuel yet to be supplied to the main fuel injection valves 79 andcapture foreign substances, dirt, and the like contained in the liquidfuel on switching wash filters. As illustrated in FIG. 10 , the mainfuel filters 131 are provided as a pair such that while one of the mainfuel filters is under maintenance, the other filter can be used.Accordingly, during driving of the engine body 21, the main fuel filters131 can be consecutively used.

As illustrated in FIG. 10 , in the pilot fuel supply path 122, asolenoid valve 172, a pilot fuel tank 171, a pilot fuel supply pump 173,maintenance valves 181 through 183, an automatic backwash filter(purification filter) 174, the pilot fuel filters 141, the pilot fuelhigh-pressure pump 56, and the pilot fuel injection valves 82 arearranged in this order from an upstream side in the flow of fuel oil.

The pilot fuel tank 171 stores liquid fuel (pilot fuel) to be suppliedto the pilot fuel injection valves 82. The pilot fuel tank 171 isdisposed separately from the liquid fuel tank 33.

The pilot fuel tank 171 and the liquid fuel tank 33 are connected toeach other by an appropriate pipe. The pipe is provided with thesolenoid valve 172. Fuel oil is supplied from the liquid fuel tank 33 tothe pilot fuel tank 171 appropriately by opening and closing thesolenoid valve 172 so that a constant amount or more of fuel oil in thepilot fuel tank 171 can be maintained.

The pilot fuel supply pump 173 is disposed downstream of the pilot fueltank 171. The pilot fuel supply pump 173 is driven by an unillustratedelectric motor to suck fuel oil in the pilot fuel tank 171 and emit theoil toward the automatic backwash filter 174. Fuel oil from whichforeign substances have been removed by the automatic backwash filter174 returns to the pilot fuel tank 171 by way of a pilot pressureretention valve 184 so that fuel oil can be continuously cleaned (thefuel purification path 123 described later). On the other hand, thepilot fuel supply path 122 includes a path that supplies fuel oilsubjected to pressure control and cleaning to the pilot fuelhigh-pressure pump 56. In this configuration, fuel oil is continuouslycleaned before supply to the pilot fuel high-pressure pump 56, and canbe supplied at a pressure necessary for the pilot fuel high-pressurepump 56. The pilot fuel supply path 122 includes the pilot fuel supplymain pipe 107, the pilot fuel supply rail pipe 47, and the pilot fuelbranch pipes 109 described above. The pilot fuel high-pressure pump 56described above is disposed in an intermediate portion of the pilot fuelsupply path 122.

Each of the pilot fuel supply main pipe 107, the pilot fuel supply railpipe 47, and the pilot fuel branch pipes 109 has a double-pipestructure, can supply fuel oil from the pilot fuel high-pressure pump 56to the pilot fuel injection valves 82 and can also return fuel oilleaked from the pilot fuel injection valves 82 to the pilot fuelhigh-pressure pump 56. Fuel oil returned from the pilot fuel injectionvalves 82 to the pilot fuel high-pressure pump 56 and fuel oil redundantin the pilot fuel high-pressure pump 56 are returned to the pilot fueltank 171 through appropriate pipes. The fuel oil returned to the pilotfuel tank 171 is not returned to the liquid fuel tank 33, and is sent tothe automatic backwash filter 174 and the pilot fuel filters 141 by thepilot fuel supply pump 173. Thus, the pilot fuel tank 171 serves as areturn tank. The fuel oil returned to the pilot fuel tank 171 may bepartially returned to the liquid fuel tank 33.

Here, a path passing through the automatic backwash filter 174 and apath bypassing the automatic backwash filter 174 are formed between thepilot fuel supply pump 173 and the pilot fuel filters 141. In the pathpassing through the automatic backwash filter 174, the maintenance valve181 and 183 are disposed upstream and downstream of the automaticbackwash filter 174. In the path bypassing the automatic backwash filter174, the maintenance valve 182 is disposed. With this configuration,when the maintenance valve 181 and the maintenance valve 183 are closedand the maintenance valve 182 is opened, no fuel flows in the automaticbackwash filter 174, and thus, maintenance can be performed on theautomatic backwash filter 174.

The pilot fuel filters 141 is disposed in an intermediate portion of thepilot fuel supply path 122 in order to remove foreign substancescontained in liquid fuel supplied as pilot fuel. Specifically, the pilotfuel filters 141 filter liquid fuel yet to be supplied to the pilot fuelinjection valves 82 and capture foreign substances, dirt, and the likecontained in the liquid fuel on interchangeable paper filters. The pilotfuel filters 141 have a filtration efficiency higher than that of theautomatic backwash filter 174 (e.g., has a smaller filter clearance, asmaller mesh; the same hereinafter). In this manner, foreign substancesor the like not filtered by the automatic backwash filter 174 can befiltered by the pilot fuel filters 141. The filtration efficiency of thepilot fuel filters 141 may be equal to that of the automatic backwashfilter 174, or may be lower than that of the automatic backwash filter174. The pilot fuel filters 141 are provided as a pair such that whileone of the pilot fuel filters is under maintenance, the other filter canbe used. Accordingly, during driving of the engine body 21, the pilotfuel filters 141 can be consecutively used. As the paper filters of thepilot fuel filters 141, filters having a higher filtration efficiencythan that of the switching wash filters of the main fuel filters 131 areused.

As described above, fuel oil to be supplied to the pilot fuel injectionvalves 82 circulates in a looped path including a looped path (fuelpurification path 123) including the pilot fuel tank 171, the pilot fuelsupply pump 173, the automatic backwash filter 174, and the pilotpressure retention valve 184, the pilot fuel filters 141, and the pilotfuel high-pressure pump 56. This path is substantially independent of apath for supplying fuel oil to the main fuel injection valves 79 of themain fuel supply path 121. Thus, while sharing the liquid fuel tank 33as a source, filtration performance of the main fuel filters 131 and thepilot fuel filters 141 can be obtained independently of each other. Withthe circulation in the looped path described above, pilot fuel oilpasses through the fine-mesh automatic backwash filter 174 and thefine-mesh pilot fuel filters 141 multiple times. Accordingly,considerably high cleanliness can be achieved for pilot fuel oil.

The engine 100 according to this embodiment includes the fuelpurification path 123. The fuel purification path 123 is a circulationpath for purifying fuel oil. Specifically, the fuel purification path123 is a path connecting the pilot fuel tank 171, the pilot fuel supplypump 173, and the automatic backwash filter 174 together in a loop. Fueloil sent from the pilot fuel tank 171 by the pilot fuel supply pump 173is purified by the automatic backwash filter 174, and is partiallyreturned to the pilot fuel tank 171 through the pilot pressure retentionvalve 184. This configuration can obtain higher cleanliness of pilotfuel oil.

The fuel purification path 123 overlaps the pilot fuel supply path 122in a section indicated by bold lines in FIG. 10 . Thus, as compared to aconfiguration in which the fuel purification path 123 is disposed not tooverlap the main fuel supply path 121, the volumes of the pilot fueltank 171, the pilot fuel supply pump 173, and the automatic backwashfilter 174, for example, can be reduced.

In the engine 100 according to this embodiment, the main fuel filters131 and the pilot fuel filters 141 are individually disposed. Thus,maintenance can be performed on the main fuel filters 131 or the pilotfuel filters 141 in accordance with frequency of use in each of thediffusion combustion system and the premixed combustion system.Consequently, the frequency of maintenance of the (fuel) filters can bereduced as a whole.

In addition, as described above, as the paper filters of the pilot fuelfilters 141, filters having a filtration efficiency higher than that ofthe switching wash filters of the main fuel filters 131 are used. Pilotfuel is supplied to the pilot fuel supply rail pipe (common rail pipe)47, and supplied to the pilot fuel injection valves 82 at high pressureto be injected in a small amount to the combustion chambers 110. Thus,the pilot fuel generally passes through pipes having small diameters.Thus, in a conventional configuration, pipes for supplying pilot fuel,clogging especially easily occurs as compared to pipes for supplyingmain fuel. In this regard, in this embodiment, the paper filters of thepilot fuel filters 141 have a filtration efficiency higher than that ofthe switching wash filters of the main fuel filters 131. Thus, cloggingof the pilot fuel can be effectively prevented or reduced, and gaseousfuel can be ignited with reliability. The filtration efficiency of thepilot fuel filters 141 may be equal to or lower than that of the mainfuel filters 131.

As the filtration efficiency of a filter increases, the costs for thefilter increases in general. In this embodiment, the pilot fuel filters141 having high filtration efficiency are disposed in the pilot fuelsupply path 122 that is a path substantially independent of the mainfuel supply path 121. Thus, a flow of fuel oil from the main fuel supplypath 121 into the pilot fuel filters 141 can be prevented or reduced,and thus, the frequency of replacement of the pilot fuel filters 141 canbe reduced. In addition, clogging is less likely to occur in theexpensive pilot fuel filters 141, costs for maintenance can be reduced.

As described above, the engine 100 according to this embodiment isoperable in the premixed combustion system in which gaseous fuel mixedwith air is caused to flow into the combustion chambers and thediffusion combustion system that injects liquid fuel into the combustionchambers for combustion. The engine 100 includes the main fuel injectionvalves 79, the pilot fuel injection valves 82, the liquid fuel tank 33,the main fuel supply path 121, the pilot fuel supply path 122, the pilotfuel filters 141, the pilot fuel high-pressure pump 56, the pilot fueltank 171, and the pilot fuel supply pump 173. The main fuel injectionvalves 79 supply liquid fuel to the combustion chambers duringcombustion in the diffusion combustion system. The pilot fuel injectionvalves 82 supply liquid fuel as pilot fuel in order to ignite gaseousfuel during combustion in the premixed combustion system. The liquidfuel tank 33 stores liquid fuel. The main fuel supply path 121 suppliesliquid fuel stored in the liquid fuel tank 33 to the main fuel injectionvalves 79. The pilot fuel supply path 122 supplies liquid fuel stored inthe liquid fuel tank 33 as pilot fuel to the pilot fuel injection valves82. The pilot fuel filters 141 are disposed in an intermediate portionof the pilot fuel supply path 122. The pilot fuel high-pressure pump 56is disposed in an intermediate portion of the pilot fuel supply path122, and sends, to the pilot fuel injection valves 82, pilot fuel thathas passed through the pilot fuel filters 141. The pilot fuel tank 171is disposed in an intermediate portion of the pilot fuel supply path122, and stores pilot fuel sent from the pilot fuel high-pressure pump56 and not injected by the pilot fuel injection valves 82. The pilotfuel supply pump 173 is disposed in an intermediate portion of the pilotfuel supply path 122, and sends pilot fuel stored in the pilot fuel tank171 to (the automatic backwash filter 174 and) the pilot fuel filters141.

Accordingly, uninjected pilot fuel does not return to the liquid fueltank 33 and is supplied to the pilot fuel injection valves 82 again.Thus, pilot fuel purified by the pilot fuel filters 141 is not easilymixed with liquid fuel in the liquid fuel tank 33. Consequently, evenwith a low cleanliness of liquid fuel stored in the liquid fuel tank 33,the maintenance frequency of the pilot fuel filters 141 can be reduced.

The engine 100 according to this embodiment also includes the fuelpurification path 123. The fuel purification path 123 is a path forcirculation through the automatic backwash filter 174 for purifyingpilot fuel and the pilot fuel tank 171.

Accordingly, pilot fuel is purified by the automatic backwash filter 174in addition to the pilot fuel filters 141, and thus, the maintenancefrequency of the pilot fuel filters 141 can be further reduced.

In the engine 100 according to this embodiment, the pilot fuel supplypath 122 and the fuel purification path partially overlap each other.

Accordingly, since the two paths overlap, the length of fuel pipes canbe reduced. In addition, a pressure loss occurring when fuel flowsthrough the fuel pipes can be reduced.

In the engine 100 according to this embodiment, the automatic backwashfilter 174 has a filtration efficiency lower than that of the pilot fuelfilters 141.

Accordingly, the pilot fuel filters 141 only need to remove foreignsubstances not removed by the automatic backwash filter 174, and thus,the maintenance frequency of the pilot fuel filters 141 can be furtherreduced.

The engine 100 according to this embodiment further includes the pilotfuel supply rail pipe 47 and the main fuel filters 131. The pilot fuelsupply rail pipe 47 is disposed in an intermediate portion of the pilotfuel supply path 122, and supplies pilot fuel to the pilot fuelinjection valves 82 at a pressure higher than that of liquid fuelsupplied to the main fuel injection valves 79. The main fuel filters 131are disposed in an intermediate portion of the main fuel supply path121. The pilot fuel filters 141 have a filtration efficiency higher thanthat of the main fuel filters 131.

Accordingly, clogging with pilot fuel injected at high pressure can bemore efficiently prevented or reduced, and gaseous fuel can be ignitedwith reliability.

Next, the following describes a variation of the embodiment withreference to FIG. 11 . FIG. 11 is a schematic view for describing a fuelsupply path that supplies fuel oil to the engine body 21 according to avariation. In a manner similar to the embodiment, the engine 100according to the variation includes a pilot fuel tank 171, and suppliesat least a part of fuel oil returned to the pilot fuel tank 171 to thepilot fuel injection valves 82 again without returning the oil to theliquid fuel tank 33.

In this variation, second pilot fuel filters 142 that are switching washfilters are disposed instead of the automatic backwash filter 174. Thesecond pilot fuel filters 142 may have any filtration efficiency, butthe filtration efficiency of the second pilot fuel filters 142 ispreferably lower than that of the pilot fuel filters 141. Common fuelfilters 190 are disposed on a path that sends fuel from the liquid fueltank 33 and a path shared by the main fuel supply path 121 and the pilotfuel supply path 122 (a path before being branched). The common fuelfilters 190 may have any filtration efficiency, but the filtrationefficiency of the common fuel filters 190 is preferably lower than thatof the main fuel filters 131. As described above, a plurality of typesof filters having different filtration efficiencies are disposed so thatthe maintenance frequency of each filter can be reduced. The number offilters disposed in the main fuel supply path 121 and the number offilters disposed in the pilot fuel supply path 122 are not limited tothe example described above, and may be changed.

In this embodiment, the pilot pressure retention valve 185 is disposedin parallel with the pilot fuel supply pump 173, and no fuelpurification path 123 is formed. The fuel purification path 123 may beomitted in this manner.

The foregoing description is directed to the preferred embodiment of thepresent invention, and the configuration described above may be changed,for example, as follows.

In the embodiment described above, the engine 100 is used as a drivingsource of a propulsive and power generating mechanism of a ship, butthis is not restrictive, and the engine 100 may be used only forpropulsion of the ship and may be used only for power generation in theship. The engine body 21 is not limited to ships, and may be placed inother moving objects or buildings.

The main fuel filters 131, the pilot fuel filters 141, and the automaticbackwash filter 174 may have different configurations from thosedescribed above as long as foreign substances or the like contained infuel can be removed. That is, the main fuel filters 131 and the pilotfuel filters 141 may be made of paper, metal, or nylon. The automaticbackwash filter 174 may be replaced by a paper filter, for example.

In the main fuel supply path 121, the main fuel pump 161 for pumpingliquid fuel (fuel oil) may be disposed downstream of the main fuelfilters 131 or upstream of the main fuel filters 131.

In the embodiment described above, the pilot fuel high-pressure pump 56is disposed downstream of the pilot fuel filters 141, but this is notrestrictive. For example, in a case where a low fuel cleanliness isrequired for the pilot fuel high-pressure pump 56, the pilot fuelhigh-pressure pump 56 may be disposed upstream of the pilot fuel filters141.

In the embodiment described above, the fuel purification path 123overlaps the main fuel supply path 121, but may not overlap the mainfuel supply path 121.

REFERENCE SIGNS LIST

-   21 engine body-   79 main fuel injection valve-   82 pilot fuel injection valve-   100 engine-   121 main fuel supply path-   122 pilot fuel supply path-   123 fuel purification path-   131 main fuel filter-   141 pilot fuel filter-   171 pilot fuel tank-   174 automatic backwash filter (purification filter)

What is claimed is:
 1. An engine operable in a premixed combustionsystem in which gaseous fuel is mixed with air is caused to flow into acombustion chamber the engine comprising: a pilot fuel injection valvethat supplies liquid fuel as pilot fuel to the combustion chamber inorder to ignite gaseous fuel during combustion in the premixedcombustion system; a liquid fuel tank that stores liquid fuel; a pilotfuel supply path that supplies liquid fuel stored in the liquid fueltank as pilot fuel to the pilot fuel injection valve; and at least twopilot fuel filters disposed in an intermediate portion of the pilot fuelsupply path.
 2. The engine according to claim 1, further comprising: apilot fuel high-pressure pump disposed in an intermediate portion of thepilot fuel supply path and configured to send pilot fuel that has passedthrough the pilot fuel filter to the pilot fuel injection valve; and apilot fuel supply pump disposed in an intermediate portion of the pilotfuel supply path.
 3. The engine according to claim 1, furthercomprising: a pilot fuel supply common rail pipe disposed in anintermediate portion of the pilot fuel supply path and configured tosupply pilot fuel to the pilot fuel injection valve.